66557591 has 4 divisors (see below), whose sum is σ = 66621384. Its totient is φ = 66493800.

The previous prime is 66557549. The next prime is 66557597. The reversal of 66557591 is 19575566.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-66557591 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66557597) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 30305 + ... + 32426.

It is an arithmetic number, because the mean of its divisors is an integer number (16655346).

Almost surely, 2^66557591 is an apocalyptic number.

66557591 is a deficient number, since it is larger than the sum of its proper divisors (63793).

66557591 is a wasteful number, since it uses less digits than its factorization.

66557591 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 63792.

The product of its digits is 283500, while the sum is 44.

The square root of 66557591 is about 8158.2835817346. The cubic root of 66557591 is about 405.2588722443.

The spelling of 66557591 in words is "sixty-six million, five hundred fifty-seven thousand, five hundred ninety-one".